Flat LED-based luminaries are expected to increasingly replace, for example, tube luminescent based luminaries. For example, flat LED-based luminaries may comprise a centrally arranged light source cavity and a wedge-shaped optical light guide in which light that is in-coupled into the light guide at the cavity travels through total internal reflection. Such luminaries involve several advantages, for example in that they are planar, compact, and relatively unobtrusive.
In case the optical light guide is surrounded by air, light can exit from both top and bottom wedge surfaces, which may not be desirable for various applications. To address this issue, WO 2008/126023 discloses a luminaire comprising a reflector arranged on one side of the light guide for reflecting the light that has escaped toward the opposite direction relative the desired exit surface. Although WO 2008/126023 provides for a compact luminaire from which light is only output through the light-exit surface, the optical properties of the luminaire, at least in its off-state, are largely determined by the properties of the reflector, which may not be desirably for all applications.